The invention relates to a thermostable polycrystalline diamond body, a method and a novel polygonal mold with walls of equal thickness for production of same. The thermostable polycrystalline diamond body of the present invention can be made into tools, such as drilling bits, wire drawing dies as well as wear-resistant components by way of high-temperature brazing or high-temperature sintering.
Conventionally, polycrystalline diamond is made by bonding diamond powder into a composite body. Due to the random orientation of the component crystals and the isotropic characteristics, a polycrystalline diamond is superior to a single crystal diamond in terms of impact resistance and wear uniformity. Tools made of polycrystalline diamond are suitable for working under more severe conditions. For instance, polycrystalline diamond cutting tools can be used for discontinuous cutting; polycrystalline diamond mining and oil drilling bits are suitable for more abrasive or broken formations; and polycrystalline wire drawing dies have an average life span 2 to 5 times that of dies made from single crystal diamond. Further because the starting material are mass produced, it is much easier and cheaper to obtain. For these reasons, there have been important developments in this field since early 1970s.
Methods of producing polycrystalline diamond have been described in U.S. Pat. No. 4,168,957 to Lee et al. and U.S. Pat. No. 3,819,814 to Pope.
Further, U.S. Pat. No. 3,913,280 to Hall, U.S. Pat. No. 3,574,580 to Stromberg, U.S. Pat. No. 4,124,401 to Lee et al. and U.S. Pat. No. 3,819,814 to Pope describe the use of silicon, its alloys or compounds as additives to improve the properties of polycrystalline diamonds.
However, none of these patents provide a thermostable polycrystalline diamond product of sufficient good quality, a method for producing thermostable polycrystalline diamond, or a method for producing a polygonal, preferably a trigonal polycrystalline diamond body with uniform wear resistance by direct molding under high pressure and high temperature.
One significant advantage of the present polycrystalline diamond product is that it has high thermostability. The product can withstand high temperatures of about 1250.degree. C. or above in a non-oxidizing atmosphere. Moreover the relative wear resistance of the polycrystalline diamond body remains the same or is improved by high temperature treatment. Because of these excellent properties, the product of the present invention can be made into tools and other articles by means of high-temperature brazing or high-temperature sintering.
The present invention provides a method of producing thermostable polycrystalline diamond bodies wherein the microstructure is different from previously known polycrystalline diamond bodies.
Conventionally, a polygonal polycrystalline diamond body is produced by cutting a large polycrystalline diamond body into the desired shape and size by means of an electric spark or a laser beam. The production cost is very high, much higher than direct molding. Trigonal or polygonal polycrystalline diamond bodies can also be produced by using a conventional mold with a round cross-section and a trigonal or polygonal cavity. However, when such a mold is used, the wear resistance of the product is not uniform, that is to say, there are variations between the wear resistance of the surfaces and the edges of the product. This results from the difference in temperature produced at the edges and on the surfaces during the high-pressure high-temperature sintering process, since the walls of the mold are not of the same thickness.